Why Does Kristen Stewart Look So Grumpy?

Maybe she's having a bad hair day. And she knows it.

Twilight lovers Rob Pattinson and Kristen Stewart dined out at Matsuhisa in Bev Hills Sunday night and, well, this isn't the first time they've gone public with their uber-private relationship.

Last Friday the couple had drinks atop the Thompson Hotel after Stewart shot an episode of Leno; earlier in the week on Tuesday night, Robsten caught a concert together at the Troubador in West Hollywood; and the night before that, the romantic twosome grabbed dinner at Ago.

What's with all the sudden PDA? Not that they were really being affectionate toward each other any of these times, but Rob and Kristen rarely go out together. Not to mention the fact that they've never confirmed their very obvious relationship! Maybe they're saving that for the Breaking Dawn red carpet premiere?

Either way, we're definitely curious as to why Ms. Stewart - a critically acclaimed actress with a hot beau and a lotta dough - looks so P.O.'d in these pix. I mean, seriously!